The Zone3 Heat Tech Neoprene Swimming Cap was made for your coldest open water swims and features 4mm neoprene together with heat-tech lining to offer you the best in warmth. The chin strap is adjustable. Key Features: Heat-tech lining for increased thermal properties Velcro strap under chin. High quality 4mm Yamamoto Smoothskin material. Part of a neoprene accessory range designed for year round training. Key Benefits: Accommodates a wide variety of head sizes. Increased warmth for your coldest open water swims. Low drag hydrodynamic design